Four South Sudanese news websites and blogs have been partially blocked, internet users and a broadcaster said on Monday, blaming it on a government crackdown on independent media.

Radio Tamazuj, a Dutch-backed radio station and website, announced on its Twitter account that it had been blocked in South Sudan. Some internet users told Reuters that the Paris-based Sudan Tribune news website was also affected on some mobile phone and Wi-Fi networks.

"This site has been blocked by South Sudan National Communication Authority," read an image forwarded to Reuters by two separate local internet users, which popped up when they tried to access the Sudan Tribune.

Others told Reuters the popular Paanluel Wel and Nyamilepedia blogs were also blocked by some internet service providers.

A National Communication Authority official who would not give his name told Reuters the order to block the websites was "government policy."

Last week, South Sudan's National Security Service arrested the director of the state television company for not transmitting a live broadcast of a speech by President Salva Kiir, according to his wife.

Earlier this year, the Foreign Correspondents Association of East Africa announced that at least 20 foreign journalists had been denied entry by authorities.

South Sudan, which won independence from Sudan in 2011, plunged into civil conflict in December 2013.